Salt

I have dyed black hair, and want to get it out to go red. So I called my hair stylist (told her my money situation.. she knows all about me.. been friends for a long time), and she told me to use some kind of salt and hot water. And to keep it on for 90 minutes. It would turn orange, and then I could add red.

My question is... what kind of salt because I thought I heard her say 'effor' salt.. but I am looking EVERYWHERE online and can't find anything.
I thought she said epsom, but she said no.. effor???
I'm confused, and she's gone on vacation for a while.
If anyone knows what she is referring to, please let me know?
Thanks so much in advance!!